It is well known in the art that wells in sandy, oil-bearing formations are frequently difficult to operate because the sand in the formation is poorly consolidated and tends to flow into the well with the oil. This "sand production" is a serious problem because the sand causes erosion and premature wearing out of the pumping equipment, and is a nuisance to remove from the oil at a later point in the production operation.
In some wells, particularly in the Saskatchewan area of Canada, oil with sand suspended therein must be pumped into large tanks for storage so that sand can settle out. Frequently, the oil can then only be removed from the upper half of the tank because the lower half of the tank is full of sand. This, too, must be removed at some time and pumped out. Moreover, fine sand is not always removed by this method and this causes substantial problems later in production operations which can lead to rejection of sand-bearing oil by the pipeline operator.
Also, removal of oil from tar sand formations is particularly challenging because high temperature steam with high pH is used. A suitable consolidating agent must withstand a similar harsh environment. In order to prevent caving around a wellbore and damage thereto, during the production of oil from a tar sand formation, it is often necessary to consolidate the formation.
Steam or fire stimulation recovery techniques are used to increase production from viscous oil-bearing formations. In steam stimulation techniques, steam is used to heat a section of the formation adjacent to a wellbore so that production rates are increased through lowered oil viscosities.
In a typical conventional steam stimulation injection cycle, steam is injected into a desired section of a reservoir or formation. A shut-in or soak phase may follow, in which thermal energy diffuses through the formation. A production phase follows in which oil is produced until oil production rates decrease to an uneconomical amount. Subsequently, injection cycles are often used to increase recovery. During the production phase, sand flowing from a subsurface formation may leave therein a cavity which may result in caving of the formation and collapse of the casing.
Caving of the formation and collapsing of the casing is not peculiar to the production of oil from a reservoir by steam stimulation. It may also occur during a water-flooding, fire-flooding, or carbon dioxide stimulation oil recovery operation.
Therefore, what is needed is a method to consolidate a formation so as to prevent caving of an interval near the wellbore which interval requires stability to withstand high pH and high temperatures during a steam stimulation or thermal oil recovery process. Similarly, prevention of caving is also required during a water-flooding or carbon dioxide stimulation oil recovery operation.